Purdue
University
Consumer Horticulture

What is Loam?

Gardeners are often advised that a loamy garden soil is best for
just about all plants. But just what is a loamy soil?

Soil is composed of many particles of varying sizes. Soil
scientists have classified soil particles into three major groups:
sand, silt and clay. Sand particles are the largest and tend to hold
little water but allow good aeration. Clay particles are very small
in size and tend to pack down so that water does not drain well and
little or no air can penetrate. Silt particles are medium sized and
have properties in between those of sand and clay.

A loamy soil, then, is one that combines all three of these types
of particles in relatively equal amounts. Loamy soil is ideal for
most garden plants because it holds plenty of moisture but also
drains well so that sufficient air can reach the roots.

Many gardeners complain of their garden soil being compacted
and/or poorly drained. Heavy, compacted soil can be rescued by the
enduring gardener. Add a good amount of organic matter, such as
compost, animal manure, cover crops or organic mulch materials, each
year as the soil is worked. It may take several years, but eventually
the soil compaction will be improved. Although adding some sand along
with the organic matter is acceptable, adding sand alone is not
advised. The organic matter offers several advantages that sand does
not, including increased water- and nutrient-holding capabilities, in
addition to improved aeration.

Highly sandy soils can be a problem since they do not hold much
water and few nutrients, as well. Adding organic materials to a sandy
soil will improve its ability to hold water and nutrients. You'll
need to add at least a two-inch layer of material to make a marked
improvement. This translates to about 17 cubic feet of organic matter
to cover a 100-square-foot area.

And remember that soil improvement is a program, not just a
one-shot deal. You'll need to continue applications at least once a
year for several years to really change the nature of the existing
soil.